This invention relates generally to a thermally actuated disconnect coupling of the type such as may be utilized in an aircraft to provide the drive connection between the output shaft of the aircraft engine gearbox and the input drive shaft of the aircraft's constant speed drive. More particularly, the invention relates to a thermally actuated disconnect which includes a fusible element such as a solder pellet located between parts of the coupling so that, when parts of the constant speed drive fail and become overheated, the pellet melts and the coupling disconnects from the gearbox thereby shutting down the constant speed drive to avoid causing excessive damage to the drive and other parts of the aircraft. In a thermally actuated disconnect coupling of the present type, a coupling shaft includes inner and outer end sections each having splines mating with the output shaft of the engine gearbox and the input drive shaft of the constant speed drive, respectively. Typically, the pellet supports the coupling shaft to hold the splines in mating engagement with each other for torque to be transmitted through the shaft from the gearbox output shaft and to the constant speed drive input shaft.
One coupling of the foregoing general character is disclosed in U.S. Pat. No. 3,889,789 and includes a dog clutch located between the inner and outer sections of the coupling shaft. When the supportive solder melts, the dog clutch between the two shaft sections disengages and the inner end section of the shaft is retracted into the driven shaft while the outer end section of the coupling shaft remains in the gearbox output shaft.